1. Field of the Invention
This invention relates to a semiconductor transcalent device and, more particularly, to a transcalent device that is cooled by a circulating liquid.
2. Description of the Prior Art
The term transcalent device is used to describe a family of high power solid state devices that include integral cooling systems. These devices are constructed to minimize the thermal resistance between a semiconductor wafer, such as silicon or germanium which is the active part of the device, and the ultimate heat sink. Such semiconductor devices include, for example, thyristors, silicon-controlled rectifiers (SCR) and transistors. All these devices produce relatively large amounts of heat, which must be effectively dissipated to prevent breakdown or destruction of the device. Different types of heat sinks have been used. One type utilizes a heat pipe structure affixed to the semiconductor wafer. In another type, to which this invention relates, liquid is circulated in close proximity to the wafer to dissipate the heat.
In a liquid cooled transcalent device using water, for example, a heated surface can typically be cooled to a temperature lower than that possible with heat pipes utilizing water as the working fluid dissipating the same amount of power. This makes liquid cooled devices very well suited for uses in applications where the devices must conduct large surges of power at a relatively small duty factor.
As is known in the art, the higher the velocity of the circulating liquid coolant, the greater the amount of heat transfer. One of the problems in attempting to achieve maximum liquid velocity is the resultant pressure losses induced. Typically, design constraints of the device are such that flow paths are not ideal and pressure losses are produced as the liquid flows through the device. The greater the pressure buildup, the more power that is needed to pump the liquid through the cooling system. In applications where pumping power is limited, cooling the device is a task of balancing the greatest velocity with the minimum pressure drop.
In addition to pressure loss problems, the uniformity of the heat transfer across the heat transfer surface is also to be considered. It is evident that the operation of a transcalent device is limited by the highest heat flux which can be dissipated at the region of lowest heat transfer or liquid velocity. A cooling system wherein the liquid velocity over the heated surface produces substantially uniform heat transfer is therefore desirable.